This invention relates to protecting conveyors carrying articles through deleterious atmospheres within chambers or booths such as spray booths.
In many industrial applications, the atmosphere within the spray booth and to which the conveyor is subjected is quite corrosive or contaminated and thus capable within a very short time of binding the moving support and drive components of the conveyor thereby dramatically increasing the power required to operate the conveyor. This of course can cause ultimate conveyor breakdown, which is quite costly both from the standpoint of the necessary repairs that must be made as well as from the loss in production during the conveyor down time, should such a conveyor be used in an assembly line.
Efforts to overcome this problem and maintain the conveyor and its moving components in a cleaner atmosphere have resulted in the shrouded and pressurized conveyor such as shown in U.S. Pat. No. 3,563,203 which discloses a conveyor having an essentially fluid impervious shroud means that substantially encloses the conveyor except for a continuous slot that parallels the support means through which the hangers fit or extend. Blower means are used to force air into and pressurize the shroud means enclosure, as compared to the atmospheric pressures ambient the shroud means. A flexible seal is used adjacent the slot to embrace the hangers and thereby generally maintain the shroud means enclosure airtight. The superatmospheric pressure in the shroud means enclosure thereby precludes the inward migration of outside atmospheric fluids and thereby maintains the moving components of the conveyor generally clean. The drawbacks of this system are apparent however in that the seal is constantly flexed by the moving hangers, which seal thus frequently fails and further which dramatically increases the conveyor drag and thus the needed input power to move the conveyor. Further, in certain atmospheres, such as in a spray chamber apparatus for paint or other coatings, the seal itself becomes loaded with the unwanted environmental fluids or paint particles which can fall onto the conveyed articles therebeneath on the conveyor hangers.
In U.S. Pat. No. 3,749,229, the flexible seal adjacent the slot was eliminated and pressurized fluid prevented unwanted environmental fluids into the shroud enclosure and the possible contact then with the moving conveyor components. However, in certain applications of this system, the pressurized fluid discharge is downwardly toward the conveyed articles on the hangers. Thus, the downward directional discharge of air onto the conveyed articles, if of sufficient velocity, can cause rippling of the uncured paint, even though the air itself is entirely pure or without suspended particles therein of appreciable size. Also, other industrial applications of shrouded and pressurized conveyor means find that the directional air discharge from the conveyor shroud enclosure toward or against the underlying conveyed articles is undesirable, particularly if the articles are close to the slot when being sprayed. Also, accumulation of dried particles, such as paint, on the conveyor parts may interfere with a good grounding of the parts passing through an electrostatic paint spray booth.